Suspension type work platforms, also commonly referred to as access platforms, are well-known in the art. Such platforms are typically powered by a hoist at each end of the platform that raises and lowers the platform on an associated suspension wire at each end. The hoists are generally very simple machines including an electric motor, a gearbox, and a traction mechanism that grips the wire. Generally the electric motors are single-speed motors; however two-speed motors are available. Traditionally the motors incorporate across-the-line starters and therefore switch from off to full speed at the press of a button. The gearboxes reduce the motor speed resulting in a platform velocity generally ranging from 27 feet per minute (fpm) to 35 fpm. Therefore, the acceleration of the work platform from standing to 27 fpm, or more, essentially instantaneously is jarring and dangerous, not only to the occupants but also the roof beams, or anchorage points.
Similarly, traditional systems offer no control over a powered deceleration of the work platform. This is particularly problematic when trying to stop the work platform at a particular elevation since the platform approaches the elevation at full speed and then stops instantaneously. This crude level of control offered by traditional systems results in repeated starting, stopping, and reversing, or “hunting,” before the desired elevation is obtained. Such repeated starts and stops not only prematurely wear the equipment, but are dangerous to the work platform occupants.
What has been missing in the art has been a system by which the users, employers, or equipment manufacturers can control the acceleration of the work platform. Further, a system in which the velocity can be adjustably limited depending on the particular working conditions is desired.